Dual Function Proppants

ABSTRACT

Proppants for use in fractured or gravel packed/frac packed oil and gas wells are provided with a contaminant removal component to remove one or more of the contaminants found in subterranean water/hydrocarbon from a production well. The water/hydrocarbon cleaning proppant solids may be used as discrete particles in a proppant formulation, as a coating on proppant solids in pores of a porous proppant solid or as part of the proppant&#39;s internal structure. The contaminant removal component removes contaminants, especially dissolved contaminants, in the subterranean water or hydrocarbon before the water/hydrocarbon leaves the well. For those contaminant removal components that can be regenerated, such as ion exchange resins, a measured quantity of an acidic regeneration solution can be injected into the fractured stratum for regeneration and recovered when the well resumes production.

This application is a continuation of copending application Ser. No.13/224,726 filed on Sep. 2, 2011 whose disclosure is incorporated hereinby reference.

FIELD OF INVENTION

The invention relates to a method for the removal of dissolvedcontaminants, especially heavy metals and naturally occurringradioactive materials (NORMs), in water and hydrocarbons produced from afractured oil or gas well as well as the composition, method ofproduction and methods for using the proppant composition in wellfracturing and production.

BACKGROUND OF THE INVENTION

Hydraulic fracturing is an often used technique to increase theefficiency and productivity of oil and gas wells. Overly simplified, theprocess involves the introduction of a water-based, oil-base or emulsionfracturing fluid into the well and the use of fluid pressure to fractureand crack the well stratum. The cracks allow the oil and gas to flowmore freely from the stratum and thereby increase production rates in anefficient manner.

There are many detailed techniques involved in well fracturing, but oneof the most important is the use of a solid “proppant” to keep thestratum cracks open as oil, gas, water and other fluids found in wellflow through those cracks. The proppant is carried into the well withthe fracturing fluid which itself may contain a variety of viscosityenhancers, gelation agents, surfactants, etc. These additives alsoenhance the ability of the fracturing fluid to carry proppant to thedesired stratum depth and location. The fracturing fluid for aparticular well may or may not use the same formulation for each depthin the stratum.

Water produced during oil and gas operations constitutes the industry'smost prolific by-product. By volume, water production representsapproximately 98 percent of the non-energy related fluids produced fromoil and gas operations, yielding approximately 14 billion barrels ofwater annually.

According to the American Petroleum Institute (API), more than 18billion barrels of waste fluids from oil and gas production aregenerated annually in the United States. Such waste materials are oftendissolved in subterranean water with a ratio of produced water to oil ofabout 10 barrels of produced water per barrel of oil. This contaminatedwater may include various ionic contaminants that include salt,hydrocarbons, heavy metals (e.g., zinc, lead, manganese, boron, copper,mercury, chromium, arsenic, strontium and aluminum), corrosive acids orbases from dissolved sulfides and sulfates, scale (e.g., insolublebarium, calcium and strontium compounds), naturally-occurringradionuclides (e.g., uranium, thorium, cadmium, radium, lead-210 anddecay products thereof) often referred to as Naturally OccurringRadioactive Materials (NORMS), sludge (oily, loose material oftencontaining silica and barium compounds) and dissolved radon gas. Ingeneral, the produced waters are re-injected into deep wells ordischarged into non-potable coastal waters. Excluding trucking costs,waste water disposal can cost as much as $2 per barrel. Such costs mustbe factored into the overall economics of a gas field.

The NORMS contaminants are a matter of particular interest. Oil and gasNORM is created in the production process, when produced fluids fromreservoirs carry sulfates up to the surface of the Earth's crust.Barium, Calcium and Strontium sulfates are larger compounds, and thesmaller atoms, such as Radium 226 and Radium 228 can fit into the emptyspaces of the compound and be carried through the produced fluids. Asthe fluids approach the surface, changes in the temperature and pressurecause the Barium, Calcium, Strontium and Radium sulfates to precipitateout of solution and form scale on the inside, or on occasion, theoutside of the completion string and/or casings. The use of thecompletion string of tubular pipes in the production process that areNORM-contaminated does not cause a health hazard if the scale is insidethe tubular string and the tubular string remain downhole. Enhancedconcentrations of the radium 226 and 228 and the degradation products(such as Lead 210) may also occur in sludge that accumulates in oilfieldpits, tanks and lagoons. Radon gas in the natural gas streams alsoconcentrate as NORM in gas processing activities. Radon decays to Lead210, then to Bismuth 210, Polonium 210 and stabilizes with Lead 206.Radon decay elements occur as a shiny film on the inner surface of inletlines, treating units, pumps and valves associated with propylene,ethane and propane processing systems.

The contaminated water produced from a well should be reused or treatedto remove the contaminants, especially the heavy metals. Oil wells arenot, however, typically located next to substantial water treatmentfacilities. The contaminated water must be captured and transported totreatment facilities or portable facilities must be brought to the well.Exemplary systems have included packed beds of activated charcoal forthe removal of organic compounds, permanent or portable ion exchangecolumns, electrodialysis and similar forms of membrane separation,freeze/thaw separation and spray evaporation, and combinations of these.All of these options are relatively costly with the water volumesproduced from a production well.

Some type of in situ treatment could be potentially very helpful tosupplement or, in some instances, replace surface-based purificationtreatments. Pointedly, it would be desirable if a proppant compositionthat is passed into the fractured well stratum could provide both acrack propping function as well as an ability to remove at least someportion of the ionic and dissolved contaminants before they wereproduced to the surface.

One publication that suggests the use of a dual function proppant isTanguay et al. WO 2010/049467. The proppant described in this publishedapplication has a polycarbodiimide or polyurethane coating thatoptionally contains organic compounds, microorganisms and petroleumprocessing catalysts. As the coating dissolves over a period of 4 hours,the compounds, microorganisms or catalyst are slowly released into thecrude oil.

U.S. Pat. No. 6,528,157 describes a coated proppant that includes afibrous material extending outwardly from the proppant coating. Thisfuzzy proppant is said to be useful for acting as a physical screen toprevent the backward flow of sand, proppants or other particles from thefractured stratum. The fibers may be any of various kinds ofcommercially available short fibers such as milled glass fibers, milledceramic fibers, milled carbon fibers and synthetic fibers having asoftening point above typical starting sand temperature for coating,e.g., at least about 200° F. so as to not degrade, soften oragglomerate.

U.S. Pat. No. 7,754,659 teaches the addition of magnetic particles onthe outside of a proppant substrate for the purpose of enhancing theflow-back resistance of the coated proppant from the fracturedsubterranean stratum.

SUMMARY OF THE INVENTION

It would be desirable to have a proppant that would act as a proppant aswell as perform filtering, cleaning or some other mode of contaminantremoval from water found within a well, especially a well for producingoil and/or gas.

It would be desirable to have an in-situ, downhole system for removingdissolved contaminants, especially dissolved forms of heavy metals andNORMs, at depth in an oil or gas well that would be effective but notmaterially increase costs or change procedures at the wellhead.

These and other objectives of the invention that will become apparentfrom the description herein can be accomplished by a proppant solidassociated with a contaminant removal component that will remove,sequester, chelate or otherwise clean at least one contaminant,especially dissolved or otherwise ionic forms of heavy metals andnaturally occurring radioactive materials (NORMS), from subterraneanwater or hydrocarbon deposits within a fractured stratum while alsopropping open cracks in said fractured stratum. Preferably, thecontaminant removal component is associated with the proppant solid as achemically distinct solid that is introduced together with the proppantsolid as an insoluble solid secured to the outer surface of the proppantsolid with a coating formulation that binds the solids together, as asolid lodged within pores of the proppant solid or as a chemicalcompound or moiety that is mixed into or integrated with a coating orthe structure of the proppant solid.

Dual function proppants according to the invention provide goodconductivity in an oil or gas production well while also removing atleast some of the impurities found in the contaminated downhole waterand hydrocarbons. Such water cleaning functions increase the value ofthe proppant by reducing the costs and/or treatment times needed tofurther clean water materials discharged from an oil or gas productionwell.

DETAILED DESCRIPTION OF THE INVENTION

The proppant of the present invention includes a proppant formulationthat comprises a contaminant removal component associated with aproppant particulate. The type of association encompasses variousphysical combinations of the proppant particulate and the contaminantremoval component, such as (a) unified proppant particulates in whichthe contaminant removal component has been integrated into the structureof the proppant particulate as a chemical compound or moiety, anadsorbed liquid or finely divided solids disposed in pores within theproppant particulate, or adhered to the outside of the proppantparticulate with a water insoluble binder coating; or (b) a physicalblend or mixture of proppant particulates and non-proppant particulates.The best choice will depend greatly on the well, the fractured stratumand the nature of the contaminants to be removed from the producedfluids.

It will be understood that the contaminant removal component that isdescribed herein for use with a proppant solid can also be used in thesame manners with other solids that are employed in well operations.Examples of such other solids include gravel packs and sand filters ofthe used in well completions. The gravel packing operation includes atransport of sand into the space between the screen and the casing, andinto the perforation tunnels. The sand is sized to prevent fineparticles or fines from the specific formation from passing through thepack (usually 20-40 mesh or 30-50 mesh or 40-60 mesh). The sand isdeposited into the annulus behind the screen and then packed to create afilter to stop the fine particulate matter or fines from migrating intothe wellbore. The screen openings are further sized to act as a finalfilter for any fines migrating through the sand bed. The contaminantremoval particles of the present invention can be readily included inphysical admixture with the gravel pack or filter sand particulates oradhered to them by way of a binder coating on the gravel pack or filtersand. They will perform additional contaminant removal as water andhydrocarbons issue from the fractured stratum.

The contaminant removal component or components can remove thecontaminants by any chemical, physical or biological method that iseffective to remove the contaminant from the subterranean waterassociated with a fractured well. The contaminant removal component inthe proppant formulation of the invention will generally exhibit afunctional affinity for the -impurities in the water/hydrocarbon phasethat pass through the fracture. Exemplary methods include ionicattraction, ionic exchange, sequestration, amalgamation, chelation,physical entrapment, absorption, adsorption, magnetic attraction, andadhesion. The specific method of removal that is most advantageous for aspecific well depends on the nature and identities of the watercontaminants that are produced from a specific well. Preferred types ofcontaminant removal components include ion exchange resins, zeolites,and chemical compounds.

Ion Exchange Resins

Synthetic ion exchange resins consist essentially of a crosslinkedpolymer network to which are attached ionized or ionizable groups. Inthe case of cation exchange resins, these groups are acidic groups(e.g., —SO₃H, —PO₃H₂, —CO₂M, and phenolic hydroxyl) while in anionexchange resins the groups are basic in character (e.g., quaternaryammonium, aliphatic or aromatic amine groups). In the synthesis of ionexchange resins, the ionizable and contaminant removal functional groupsmay be attached to the monomers or intermediates used in preparation ofthe crosslinked polymer, or they may be introduced subsequently into apreformed polymer.

Cation exchange resins are prepared by sulfonatingstyrene-divinylbenzene copolymers as described in U.S. Pat. No.2,366,007. Many strongly basic anion exchange resins are prepared bytreating crosslinked polystyrene with chloromethyl ether in the presenceof a Friedel-Crafts catalyst. The chloromethylated product is thentreated with a tertiary amine, e.g., trimethylamine, to give a resincontaining strongly basic quaternary ammonium groups. The crosslinkedpolystyrene is generally a copolymer with up to about 10%divinylbenzene.

Suitable ion exchange resins for the present invention are generallycategorized as strong acid cation exchange resins, weak acid cationexchange resins, strong base anion exchange resins, and weak base anionexchange resins.

Ion exchange resins can be physically blended with proppant solidsgenerally within the weight ratio range of about 1000:1 to about 1:1000of exchange resin to proppant. The specific weight ratio will depend onthe relative densities of these materials, the carrying capacity of theresin and the contaminants found downhole. Generally, ion exchangeresins within the range of about 10-60 mesh (250-2000 μm) are suitablefor physical admixtures with proppant solids. Alternatively, ionexchange resin solids can be disposed within pore openings or bound tothe proppant solid with an exterior coating, adhesive or binder thatresists dissolution under downhole conditions. Ion exchange resinswithin the range of about 10-400 mesh (38-2000 μm) are generallysuitable for such combinations. Even smaller sizes can be used to meetthe requirements of small pores within the proppant particulate.

Ion exchange resins are likely to become spent as they are used tocollect contaminants. These resins can be regenerated in situ byinjecting an acidic solution into the fractured stratum containing theexchange resin. After a suitable recharge period, the discharge waterthat is laden with flushed contaminants is recovered as the well resumesproduction. See U.S. Pat. No. 7,896,080 whose disclosure is herebyincorporated by reference.

Molecular Sieves and Zeolites

Compositionally, zeolites are similar to clay minerals. Morespecifically, both are alumino-silicates. They differ, however, in theircrystalline structure. Many clays have a layered crystalline structure(similar to a deck of cards) and are subject to shrinking and swellingas water is absorbed and removed between the layers. In contrast,zeolites have a rigid, 3-dimensional crystalline structure (similar to ahoneycomb) consisting of a network of interconnected tunnels and cages.Water moves freely in and out of these pores but the zeolite frameworkremains rigid. Another special aspect of this structure is that the poreand channel sizes are nearly uniform, allowing the crystal to act as amolecular sieve. The porous zeolite is host to water molecules and ionsof potassium and calcium, as well as a variety of other positivelycharged ions, but only those of appropriate molecular size to fit intothe pores are admitted creating the “sieving” property.

One important property of zeolite is the ability to exchange cations.This is the trading of one charged ion for another on the crystal. Onemeasure of this property is the cation exchange capacity. Zeolites havehigh cation exchange capacities, arising during the formation of thezeolite from the substitution of an aluminum ion for a silicon ion in aportion of the tetrahedral units that make up the zeolite crystal. SeeU.S. Pat. Nos. 2,653,089; 5,911,876; 7,326,346; 7,884,043 and PublishedUS Patent Application Nos. 2004/010267 and 2005/018193. Other molecularsieves and adsorbents have been synthesized that appear to work wellwith NORMS-type contaminants. See U.S. Pat. No. 7,332,089 and 7,537,702.The disclosures of each of these references are hereby incorporated byreference.

Suitable molecular sieves and zeolites for use in the present inventioninclude pretreated or untreated natural and synthetic molecular sieveswith pore size and exchange characteristics suitable for the contaminantto be removed, e.g., heavy metals. Examples of such zeolites includealuminosilicates such as clinoptilolite, modified clinoptilolite perU.S. Pat. No. 7,074,257, vermiculite, montmorillonite, bentonite,chabazite, heulandite, stilbite, natrolite, analcime, phillipsite,permatite, hydrotalcite, zeolites A, X, and Y; antimonysilicates;silicotitanates; and sodium titanates.

Chemicals

Porous proppant particulates can be impregnated with one or morechemical compounds that have an affinity for binding with thecontaminant targeted for removal. Examples of chemical compounds with anaffinity for different contaminants include sulfonic acids, carboxylicacids, phenolics, aminoacids, glycolamines, polyamines, quaternaryamines, polyhydroxylic compounds, and combinations thereof. Thisfunctionality should be primarily available at the surface of the coatedparticles to enhance contact with the ionic contaminant species andremoval from solution.

Other Contaminant Removal Components

In addition to the above, contaminants from water and hydrocarbons foundin a fractured stratum can include activated carbon, non-molecular sieveadsorbent solids with an affinity for heavy metals and reactivematerials that will form insoluble complexes or amalgams with thetargeted metal ion contaminant species.

Proppant Solids

Proppant solids can be virtually any small solid or porous with anadequate crush strength and lack of chemical reactivity. Suitableexamples include sand, ceramic particles (such as aluminum oxide,silicon dioxide, titanium dioxide, zinc oxide, zirconium dioxide, ceriumdioxide, manganese dioxide, iron oxide, calcium oxide or bauxite) whichmay or may not embody the contaminant removal component as an integralcomponent of the ceramic matrix or structure, or also other granularmaterials. Proppant materials that have been widely used include: (1)particulate sintered ceramics, typically aluminum oxide, silica, orbauxite, often with clay-like binders or other additives to increase theparticulate's compressive strength, especially sintered bauxite; (2)natural, relatively coarse, sand, the particles of which are roughlyspherical, generally called “frac sand”; (3) resin-coated particulatesof these materials and (4) composite particles or composite particlescontaining a solid or porous solid core in which the contaminant removalagent is an integral part of the solid core or disposed within pores ofthe porous solid core. The proppants to be coated preferably have anaverage particle size within the range from about 50 μm and about 3000μm, and more preferably within the range from about 100 μm to about 2000μm.

The proppant should have a distribution of particles having sizes in therange of from about 4 mesh to about 100 mesh (U.S. Standard Sievenumbers), i.e., the particles pass through a screen opening of about4760 microns (4 mesh) and are retained on a screen opening of about 150microns (100 mesh). Preferred proppants have a distribution of particlesizes in which 90% are within the range of 8 mesh to 100 mesh, and moreusually in the range of 16 mesh to 70 mesh. Particularly preferredproppants have a distribution of particle sizes with at least 90% byweight of the particles having a size within a desired range, such asthe range of 20 mesh to 40 mesh, i.e., between about 850 and about 425microns.

Coatings

A coating can be used to provide exposed surface moieties of the typesnoted above that have an affinity for removing contaminants or thecoating can be used as an insoluble binder to secure or adhere aparticulate contaminant removal component to the outer surface of theproppant solid. Coatings can be cured, partially cured or uncured andare intended to secure the contaminant removal component to the proppantsolid. Which of these forms is most desirable for a particular well willdepend on the coating, its dissolution characteristics in the downholeenvironment, and the nature of the cleaning component.

Coatings used to bind the contaminant removal agent and the proppantsolid can use virtually any coating formulation but preferably usecoating formulations previously used to help consolidate or improve thestrength of the proppant within the fractured stratum and resistwashout. Thermoset and thermoplastic resins are common. Hot meltadhesives have been proposed for use based on a theory of operation thatthe coating on the proppant will exhibit a latent tackiness, i.e., thetackiness of the coating does not develop until the proppant is placedinto the hydrocarbon-bearing formation. Within the downhole environment,the subterranean heat causes the adhesive to become tacky so thataggregation occurs as the coating softens to cause the tacky adhesivethermoplastic to produce stable agglomerates within the fracturedsubterranean formation.

Resin coated proppants come in three types: precured, partially curedand curable. Precured resin coated proppants comprise a substrate coatedwith a resin which has been significantly crosslinked. The resin coatingof the precured proppants provides crush resistance to the substrate.Since the resin coating is already cured before it is introduced intothe well, even under high pressure and temperature conditions, theproppant does not agglomerate and is capable of generating substantialparticle to particle bond strength. Such precured resin coated proppantsare typically held in the fracture by the stress surrounding them. Theresin coating of a partially cured proppant has been partially reactedduring the manufacturing process but retains a significant level ofcurability. The resin coating of the curable proppants is notsignificantly crosslinked or cured before injection into the oil or gaswell. The partially cured and curable coatings are designed to crosslinkunder the stress and temperature conditions existing in the wellformation. This causes the proppant particles to bond together forming a3-dimensional matrix and preventing proppant flow-back.

Suitable coatings include 0.1-10 wt % of a cured, partially cured orcurable organic polymer, prepolymer, and oligomer of resole or novolactype. The specific chemistries of such organic coatings can be chosenfrom a wide selection, including epoxy, phenolic, polyurethane,polycarbodiimide, furan resins and combinations of these with eachother. The phenolics of the above-mentioned novolac or resole polymersmay be phenol moieties or bis-phenol moieties. Novolac resins arepreferred. Specific thermoplastics include polyethylene,acrylonitrile-butadiene styrene, polystyrene, polyvinyl chloride,fluoroplastics, polysulfide, polypropylene, styrene acrylonitrile,nylon, and phenylene oxide. Specific thermosets include epoxy, phenolic,e.g., resole (a true thermosetting resin) or novolac (thermoplasticresin which is rendered thermosetting by a hardening agent), polyesterresin, polyurethanes and derivatives thereof, and epoxy-modifiednovolac. The phenolic resin comprises any of a phenolic novolac polymer;a phenolic resole polymer; a combination of a phenolic novolac polymerand a phenolic resole polymer; a cured combination of phenolic/furanresin or a furan resin to form a precured resin.

A preferred proppant coating for use in the present invention includes asubstantially homogeneous mixture that comprises: (a) an isocyanatereactant, (b) a polyol reactant which may or may not have reactive aminefunctionality, (c) optionally, an amine reactant that is different fromthe polyol reactant, and (d) optionally, an amine-based, latent curingagent. A typical proppant resin is a phenolic novolac resin coatingcomposition combined with hexamethylenediaminetetramine (HEXA),formaldehyde, paraformaldehyde, oxazolidines, phenol-aldehyde resolepolymers and/or other known curing agents as a cross-linking agent toachieve a precured or curable proppant.

The coating process of the present invention applies one or more layersof substantially cured polyurethane around a solid proppant core. Thecoating is cured and crosslinked to the point that it can resistdissolution under the rigorous combination of high heat, agitation,abrasion and water found downhole in a well. Preferably, thesubstantially cured coating exhibits a sufficient resistance to a 10 dayautoclave test or 10 day conductivity test so that the coating resistsloss by dissolution in hot water (“LOI loss”) of less than 25 wt %, morepreferably less than 15 wt %, and even more preferably a loss of lessthan 5 wt %. The substantially cured coating of the invention thusresists dissolution in the fractured stratum while also exhibitingsufficient resistance to flow back and sufficiently high crush strengthto maintain conductivity of the fractures.

A preferred testing method for is described in ISO 13503-5:2006(E)“Procedures for measuring the long term conductivity of proppants”, thedisclosure of which is herein incorporated by reference. ISO13503-5:2006 provides standard testing procedures for evaluatingproppants used in hydraulic fracturing and gravel packing operations.ISO 13503-5:2006 provides a consistent methodology for testing performedon hydraulic fracturing and/or gravel packing proppants. The “proppants”mentioned henceforth in this part of ISO 13503-5:2006 refer to sand,ceramic media, resin-coated proppants, gravel packing media, and othermaterials used for hydraulic fracturing and gravel-packing operations.ISO 13503-5:2006 is not applicable for use in obtaining absolute valuesof proppant pack conductivities under downhole reservoir conditions, butit does serve as a consistent method by which such downhole conditionscan be simulated and performance properties of proppant compared in alaboratory setting.

The isocyanate component comprises an isocyanate with at least 2reactive isocyanate groups. Other isocyanate-containing compounds may beused, if desired. Examples of suitable isocyanate with at least 2isocyanate groups an aliphatic or an aromatic isocyanate with at least 2isocyanate groups (e.g. a diisocyanate, triisocyanate ortetraisocyanate), or an oligomer or a polymer thereof can preferably beused. These isocyanates with at least 2 isocyanate groups can also becarbocyclic or heterocyclic and/or contain one or more heterocyclicgroups.

The isocyanate with at least 2 isocyanate groups is preferably acompound of the formula (III) or a compound of the formula (IV):

In the formulas (III) and (IV), A is each, independently, an aryl,heteroaryl, cycloalkyl or heterocycloalkyl. Preferably, A is each,independently, an aryl or cycloalkyl. More preferably A is each,independently, an aryl which is preferably phenyl, naphthyl oranthracenyl, and most preferably phenyl. Still more preferably A is aphenyl.

The above mentioned heteroaryl is preferably a heteroaryl with 5 or 6ring atoms, of which 1, 2 or 3 ring atoms are each, independently, anoxygen, sulfur or nitrogen atom and the other ring atoms are carbonatoms. More preferably the heteroaryl is selected among pyridinyl,thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl,pyridazinyl, oxazolyl, isoxazolyl or furazanyl.

The above mentioned cycloalkyl is preferably a C₃₋₁₀-cycloalkyl, morepreferably a C₅₋₇-cycloalkyl.

The above mentioned heterocycloalkyl is preferably a heterocycloalkylwith 3 to 10 ring atoms (more preferably with 5 to 7 ring atoms), ofwhich one or more (e.g. 1, 2 or 3) ring atoms are each, independently,an oxygen, sulfur or nitrogen atom and the other ring atoms are carbonatoms. More preferably the heterocycloalkyl is selected from amongtetrahydrofuranyl, piperidinyl, piperazinyl, aziridinyl, acetidinyl,pyrrolidinyl, imidazolidinyl, morpholinyl, pyrazolidinyl,tetrahydrothienyl, octahydroquinolinyl, octahydroisoquinolinyl,oxazolidinyl or isoxazolidinyl. Still more preferably, theheterocycloalkyl is selected from among tetrahydrofuranyl, piperidinyl,piperazinyl, pyrrolidinyl, imidazolidinyl, morpholinyl, pyrazolidinyl,tetrahydrothienyl, oxazolidinyl or isoxazolidinyl.

In the formulas (III) and (IV), each R¹ is, independently, a covalentbond or C₁₋₄-alkylene (e.g. methylene, ethylene, propylene or butylene).

In the formulas (III) and (IV), each R² is each, independently, ahalogen (e.g. F, Cl, Br or I), a C₁₋₄-alkyl (e.g. methyl, ethyl, propylor butyl) or C₁₋₄-alkyoxy (e.g. methoxy, ethoxy, propoxy or butoxy).Preferably, each R² is, independently, a C₁₋₄-alkyl. More preferablyeach R² is methyl.

In the formula (IV), R³ is a covalent bond, a C₁₋₄-alkylene (e.g.methylene, ethylene, propylene or butylene) or a group—(CH₂)_(R31)—O—(CH₂)_(R32)—, wherein R31 and R32 are each,independently, 0, 1, 2 or 3. Preferably, R³ is a —CH₂— group or an —O—group.

In the formula (III), p is equal to 2, 3 or 4, preferably 2 or 3, morepreferably 2.

In the formulas (III) and (IV), each q is, independently, an integerfrom 0 to 3, preferably 0, 1 or 2. When q is equal to 0, thecorresponding group A has no substitutent R², but has hydrogen atomsinstead of R².

In the formula (IV), each r and s are, independently, 0, 1, 2, 3 or 4,wherein the sum of r and s is equal to 2, 3 or 4. Preferably, each r ands are, independently, 0, 1 or 2, wherein the sum of r and s is equal to2. More preferably, r is equal to 1 and s is equal to 1.

Examples of the isocyanate with at least 2 isocyanate groups are:toluol-2,4-diisocyanate; toluol-2,6-diisocyanate;1,5-naphthalindiisocyanate; cumol-2,4-diisocyanate;4-methoxy-1,3-phenyldiisocyanate; 4-chloro-1,3-phenyldiisocyanate;diphenylmethane-4,4-diisocyanate; diphenylmethane-2,4-diisocyanate;diphenylmethane-2,2-diisocyanate; 4-bromo-1,3-phenyldiisocyanate;4-ethoxy-1,3-phenyl-diisocyanate; 2,4′-diisocyanate diphenylether;5,6-dimethyl-1,3-phenyl-diisocyanate;2,4-dimethyl-1,3-phenyldiisocyanate; 4,4-diisocyanato-diphenylether;4,6-dimethyl-1,3-phenyldiisocyanate; 9,10-anthracene-diisocyanate;2,4,6-toluol triisocyanate; 2,4,4′-triisocyanatodiphenylether;1,4-tetramethylene diisocyanate; 1,6-hexamethylene diisocyanate;1,10-decamethylene-diisocyanate; 1,3-cyclohexylene diisocyanate;4,4′-methylene-bis-(cyclohexylisocyanate); xylol diisocyanate;1-isocyanato-3-methyl-isocyanate-3,5,5-trimethylcyclohexane (isophoronediisocyanate); 1-3-bis(isocyanato-1-methylethyl)benzol (m-TMXDI);1,4-bis(isocyanato-1-methylethyl) benzol (p-TMXDI); oligomers orpolymers of the above mentioned isocyanate compounds; or mixtures of twoor more of the above mentioned isocyanate compounds or oligomers orpolymers thereof.

Particularly preferred isocyanates with at least 2 isocyanate groups aretoluol diisocyanate, diphenylmethane diisocyanate, an oligomer based ontoluol diisocyanate or an oligomer based on diphenylmethanediisocyanate.

A polyol component can be added to the coating formulation. The polyolcomponent may or may not have reactive amine functionality. Anespecially preferred polyurethane coating is a phenolic polyurethanemade with a phenolic polyol according to a patent application that wasfiled with the German Patent Office under no. DE 10 2010 051 817.4 onNov. 19, 2010 and entitled “Proppant Coating Technology”, the disclosureof which is herein incorporated by reference and summarized below in thecontext of the process of the present invention.

Another preferred polyol component for the present process comprises aphenol resin that comprises a condensation product of a phenol and analdehyde, such as formaldehyde. The phenol resin is preferably a resoleor novolak phenol resin and more preferably a benzyl ether resin.

The resole-type phenol resin can be obtained, for example, bycondensation of phenol or of one or more compounds of the followingformula (I), with aldehydes, preferably formaldehyde, under basicconditions.

In the formula (I):

-   -   “R” is in each case, independently, a hydrogen atom, a halogen        atom, C₁₋₁₆-alkyl (preferably C₁₋₁₂-alkyl, more preferably        C₁₋₆-alkyl, and still more preferably methyl, ethyl, propyl or        butyl) or —OH;    -   “p” is an integer from 0 to 4, preferably 0, 1, 2 or 3, and more        preferably 1 or 2. Those in the art will understand that when p        is 0, the compound of formula (I) is phenol.

Novolak-type phenol resin for the present invention comprises thecondensation product of phenol or of one or more compounds of theformula (I) defined above, with aldehydes, preferably formaldehyde,under acidic conditions.

In another preferred embodiment, the phenol resin is a benzyl etherresin of the general formula (II):

In the formula (II):

-   -   A, B and D each are, independently, a hydrogen atom, a halogen        atom, a C₁₋₁₆-hydrocarbon residue, —(C₁₋₁₆-alkylene)-OH, —OH, an        —O—(C₁₋₁₆-hydrocarbon residue), phenyl, —(C₁₋₆-alkylene)-phenyl,        or —(C₁₋₆-alkylene)-phenylene-OH;    -   The halogen atom is F, Cl, Br or I;    -   The C₁₋₁₆-hydrocarbon-residue is preferably C₁₋₁₆-alkyl,        C₂₋₁₆-alkenyl or C₂₋₁₆-alkinyl, more preferably C₁₋₁₂-alkyl,        C₂₋₁₂-alkenyl or C₂₋₁₂-alkinyl, still more preferably        C₁₋₆-alkyl, C₂₋₆-alkenyl or C₂₋₆-alkinyl, and still more        preferably C₁₋₄-alkyl, C₂₋₄-alkenyl or C₂₋₄-alkinyl, and still        more preferably C₁₋₁₂-alkyl, and still more preferably        C₁₋₆-alkyl, and still more preferably methyl, ethyl, propyl or        butyl, and most preferably methyl;    -   The residue —(C₁₋₁₆-alkylene)-OH is preferably        —(C₁₋₁₂-alkylene)-OH, more preferably —(C₁₋₆-alkylene)-OH, and        still more preferably —(C₁₋₄-alkylene)-OH, and most preferably a        methylol group (—CH₂—OH);    -   The —O—(C₁₋₁₆-hydrocarbon)-residue is preferably C₁₋₁₆-alkoxy,        more preferably C₁₋₁₂-alkoxy, and still more preferably        C₁₋₆-alkoxy, and still more preferably C₁₋₄-alkoxy, and still        more preferably —O—CH₃, —O—CH₂CH₃, —O—(CH₂)₂CH₃ or —O—(CH₂)₃CH₃;    -   The residue —(C₁₋₆-alkylene)-phenyl is preferably        —(C₁₋₄-alkylene)-phenyl, and more preferably —CH₂-phenyl;    -   The residue —(C₁₋₆-alkylene)-phenylene-OH is preferably        —(C₁₋₄-alkylene)-phenylene-OH, and more preferably        —CH₂-phenylene-OH;    -   R is a hydrogen atom of a C₁₋₆-hydrocarbon residue (e.g. linear        or branched C₁₋₆-alkyl). R is particularly preferred as a        hydrogen atom. This is the case, for example, when formaldehyde        is used as aldehyde component in a condensation reaction with        phenols in order to produce the benzyl ether resin of the        formula (II);    -   m¹ and m² are each, independently, 0 or 1.    -   n is an integer from 0 to 100, preferably an integer from 1 to        50, more preferably from 2 to 10, and still more preferably from        2 to 5; and    -   wherein the sum of n, m¹ and m² is at least 2.

In a still further embodiment, the polyol component is a phenol resinwith monomer units based on cardol and/or cardanol. Cardol and cardanolare produced from cashew nut oil which is obtained from the seeds of thecashew nut tree. Cashew nut oil consists of about 90% anacardic acid andabout 10% cardol. By heat treatment in an acid environment, a mixture ofcardol and cardanol is obtained by decarboxylation of the anacardicacid. Cardol and cardanol have the structures shown below:

As shown in the illustration above, the hydrocarbon residue(—C₁₅H_(31-n)) in cardol and/or in cardanol can have one (n=2), two(n=4) or three (n=6) double bonds. Cardol specifically refers tocompound CAS-No. 57486-25-6 and cardanol specifically to compoundCAS-No. 37330-39-5.

Cardol and cardanol can each be used alone or at any particular mixingratio in the phenol resin. Decarboxylated cashew nut oil can also beused.

Cardol and/or cardanol can be condensed into the above described phenolresins, for example, into the resole- or novolak-type phenol resins. Forthis purpose, cardol and/or cardanol can be condensed e.g. with phenolor with one or more of the above defined compounds of the formula (I),and also with aldehydes, preferably formaldehyde.

The amount of cardol and/or cardanol which is condensed in the phenolresin is not particularly restricted and preferably is from about 1 wt %to about 99 wt %, more preferably about 5 wt % to about 60 wt %, andstill more preferably about 10 wt % to about 30 wt %, relative to 100 wt% of the amount of phenolic starting products used in the phenol resin.

In another embodiment, the polyol component is a phenol resin obtainedby condensation of cardol and/or cardanol with aldehydes, preferablyformaldehyde.

A phenol resin which contains monomer units based on cardol and/orcardanol as described above, or which can be obtained by condensation ofcardol and/or cardanol with aldehydes, has a particularly low viscosityand can thus preferably be employed with a low addition or withoutaddition of reactive thinners. Moreover, this kind of long-chain,substituted phenol resin is comparatively hydrophobic, which results ina favorable shelf life of the coated proppants obtained by the methodaccording to the present invention. In addition, a phenol resin of thiskind is also advantageous because cardol and cardanol are renewable rawmaterials.

Apart from the phenol resin, the polyol component can still containother compounds containing hydroxyl groups. The other compoundscontaining hydroxyl groups can be selected from the compounds containinghydroxyl groups that are known to be useful for making polyurethanes,e.g., hydroxy-functional polyethers, hydroxy-functional polyesters,alcohols or glycols. One preferred compound containing hydroxyl groupsis, for instance, castor oil. Compounds containing hydroxyl groups suchas alcohols or glycols, in particular cardol and/or cardanol, can beused as reactive thinners.

The amount of the other compounds containing hydroxyl groups depends onthe desired properties of the proppant coating and can suitably beselected by the person skilled in the art. Typical amounts of compoundscontaining hydroxyl groups are in the range of between about 10 wt % andabout 80 wt %, preferably from about 20 wt % to about 70 wt %, relativeto 100 wt % of the polyol component.

The process of the present invention is particularly useful when theproppants are coated with a condensation reaction product that has beenmade with an excess of isocyanate component with respect to the polyolcomponent. In step (a) therefore, 1 part by weight of the polyolcomponent is used at an amount within the range from about 100 wt % toabout 10,000 wt %, preferably about 105 wt % to about 5,000 wt %, morepreferably about 120 wt % to about 3000 wt %, and still more preferablyabout 130 wt % to about 1000 wt %, of the isocyanate base value.

The isocyanate base value defines the amount of the isocyanate componentwhich is equivalent to 100 parts by weight of the polyol component. TheNCO-content (%) of the isocyanate component is defined herein accordingto DIN ISO 53185. To determine the OH-content (%) of the polyolcomponent, first the so-called OH-number is determined in mg KOH/gaccording to DIN ISO 53240 and this value is divided by 33, in order todetermine the OH-content.

Moreover, in step (a) one or more additives can be mixed with theproppant, the polyol component and the isocyanate component. Theseadditives are not particularly restricted and can be selected from theadditives known in the specific field of coated proppants. Provided thatone of these additives has hydroxyl groups, it should be considered as adifferent hydroxyl-group-containing compound, as described above inconnection with the polyol component. If one of the additives hasisocyanate groups, it should be considered as a differentisocyanate-group-containing compound. Additives with hydroxyl groups andisocyanate groups can be simultaneously considered as differenthydroxyl-group-containing compounds and as differentisocyanate-group-containing compounds.

Attaching the functionality that provides the cleaning property couldrequire an additive which is (a) reactive with the isocyanate or (b)reactive with the polyol or (c) reactive with the curing agent to beused. Thus, additives (or combinations of additives) such asethanolamines, aminoacids, phenolsulfonic acids, salicylates, andquaternary ammonium compounds can be introduced into or into theproppant as an additive in the coating process whereby the removalcomponent with water cleaning functionality is directly incorporatedinto the coating of the proppant.

It may also be possible to incorporate the removal component as anadditive that already possesses the ability to clean water/hydrocarbon,wherein the coating on the proppant functions to sstick the additive tothe surface of the proppant, enabling the dual action of propping andwater/hydrocarbon cleaning to act. Examples of this type would be afinely powdered form of commercial water treatment resins, such as anionexchange resins, cation exchange resins, and/or chelating ion exchangeresins.

Alternatively, a physical blend of the coated or uncoated proppantparticles and ion exchange resins beads can be used in the fracturingprocess as a means of introducing the combination of proppants andwater/hydrocarbon cleaning activity that is required. This physicalblend could consolidate in the fracture to immobilize the ion exchangeresin beads, thus creating a capability to clean the fluid passingthrough the pack within the fracture.

A preferred proppant product would be a blend of compositionallydifferent proppant solids and/or proppant properties. For example, someproppants would be formulated to remove one type of contaminant whileother proppant solids in the blend would target a different contaminant.The ratio of a coated proppant solid blend can vary broadly within therange from about 1:1000 to 1000:1.

The coating formulation of the present invention may also include areactive amine component that is different from the polyol reactant.Preferably, the reactive amine component is an amine-terminatedcompound. This component enhances crosslink density within the coatingand, depending on component selection, can provide additionalcharacteristics of benefit to the cured coating. Particularly preferredreactive amine components for use in the present invention includeamine-terminated compounds such as diamines, triamines, amine-terminatedglycols such as the amine-terminated polyalkylene glycols soldcommercially under the trade name JEFFAMINE from Huntsman PerformanceProducts in The Woodlands, Tex.

Suitable diamines include primary, secondary and higher polyamines andamine-terminated compounds. Suitable compounds include, but are notlimited to, ethylene diamine; propylenediamine; butanediamine;hexamethylenediamine; 1,2-diaminopropane; 1,4-diaminobutane;1,3-diaminopentane; 1,6-diaminohexane; 2,5-diamino-2,5-dimethlhexane;2,2,4- and/or 2,4,4-trimethyl-1,6-diaminohexane; 1,11-diaminoundecane;1,12-diaminododecane; 1,3- and/or 1,4-cyclohexane diamine;1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane; 2,4- and/or2,6-hexahydrotoluylene diamine; 2,4′ and/or 4,4′-diaminodicyclohexylmethane and 3,3′-dialkyl-4,4′-diamino-dicyclohexyl methanes such as3,3′-dimethyl-4,4-diamino-dicyclohexyl methane and3,3′-diethyl-4,4′-diaminodicyclohexyl methane; aromatic polyamines suchas 2,4- and/or 2,6-diaminotoluene and 2,6-diaminotoluene and 2,4′ and/or4,4′-diaminodiphenyl methane; and polyoxyalkylene polyamines (alsoreferred to herein as amine terminated polyethers).

Mixtures of polyamines may also be employed in preparing asparticesters, which is a secondary amine derived from a primary polyamine anda dialkyl maleic or fumaric acid ester, for use in the invention.Representative examples of useful maleic acid esters include dimethylmaleate, diethyl maleate, dibutyl maleate, dioctyl maleate, mixturesthereof and homologs thereof.

Suitable triamines and higher multifunctional polyamines for use in thepresent coating include diethylene triamine, triethylenetetramine, andhigher homologs of this series.

JEFFAMINE diamines include the D, ED, and EDR series products. The Dsignifies a diamine, ED signifies a diamine with a predominatelypolyethylene glycol (PEG) backbone, and EDR designates a highlyreactive, PEG based diamine.

JEFFAMINE D series products are amine terminated polypropylene glycolswith the following representative structure:

JEFFAMINE ® x MW* D-230 ~2.5 230 D-400 ~6.1 430 D-2000 ~33 2,000 D-4000(XTJ-510) ~68 4,000

JEFFAMINE EDR-148 (XTJ-504) and JEFFAMINE EDR-176 (XTJ-590) amines aremuch more reactive than the other JEFFAMINE diamines and triamines. Theyare represented by the following structure:

JEFFAMINE ® y x + z MW* HK-511 2.0 ~1.2 220 ED-600 (XTJ-500) ~9.0 ~3.6600 ED-900 (XTJ-501) ~12.5 ~6.0 900 ED-2003 (XTJ-502) ~39 ~6.0 2,000

JEFFAMINE T series products are triamines prepared by reaction ofpropylene oxide (PO) with a triol intiator followed by amination of theterminal hydroxyl groups. They are exemplified by the followingstructure:

Moles PO JEFFAMINE ® R n (x + y + z) MW* T-403 C₂H₅ 1 5-6  440 T-3000(XTJ-509) H 0 50 3000 T-5000 H 0 85 5000

The SD Series and ST Series products consist of secondary amine versionsof the JEFFAMINE core products. The SD signifies a secondary diamine andST signifies a secondary trimine. The amine end-groups are reacted witha ketone (e.g. acetone) and reduced to create hindered secondary amineend groups represented by the following terminal structure:

One reactive hydrogen on each end group provides for more selectivereactivity and makes these secondary di- and triamines useful forintermediate synthesis and intrinsically slower reactivity compared withthe primary JEFFAMINE amines.

JEFFAMINE® Base Product MW* SD-231 (XTJ-584) D-230 315 SD-401 (XTJ-585)D-400 515 SD-2001 (XTJ-576) D-2000 2050 ST-404 (XTJ-586) T-403 565

See also U.S. Pat. Nos. 6,093,496; 6,306,964; 5,721,315; 7,012,043; andPublication U.S. Patent Application No. 2007/0208156 the disclosure ofwhich are hereby incorporated by reference.

An amine-based latent curing agent may optionally be added to thecoating formulation with the isocyanate component, the polyol component,the amine-reactive polyol component or added simultaneously as any ofthese components or pre-coated on the proppant. Suitable amine-basedlatent curing agents for use with the present invention includetriethylenediamine; bis(2-dimethylaminoethyl)ether;tetramethylethylenediamine; pentamethyldiethylenetriamine; and othertertiary amine products of alkyleneamines. Additionally, other catalyststhat promote the reaction of isocyanates with hydroxyls and amines thatare known by the industry can be used in the present invention.

Amine-based latent curing agents may be added in an amount within therange from about 0.1 to about 10% by weight relative to the total weightof the coating resin.

The proppant coating compositions of the invention may also includevarious additives. For example, the coatings of the invention may alsoinclude pigments, tints, dyes, and fillers in an amount to providevisible coloration in the coatings. Other materials conventionallyincluded in coating compositions may also be added to the compositionsof the invention. These additional materials include, but are notlimited to, reaction enhancers or catalysts, crosslinking agents,optical brighteners, propylene carbonates, coloring agents, fluorescentagents, whitening agents, UV absorbers, hindered amine lightstabilizers, defoaming agents, processing aids, mica, talc, nano-fillersand other conventional additives. All of these materials are well knownin the art and are added for their usual purpose in typical amounts. Forexample, the additives are preferably present in an amount of about 15weight percent or less. In one embodiment, the additive is present in anamount of about 5 percent or less by weight of the coating composition.

Other additives can include, for example, solvents, softeners,surface-active agents, molecular sieves for removing the reaction water,thinners and/or adhesion agents can be used. Silanes are a particularlypreferred type of adhesion agent that improves the affinity of thecoating resin for the surface of the proppant. Silanes can be mixed inas additives in step (a), but can also be converted chemically withreactive constituents of the polyol component or of the isocyanatecomponent. Functional silanes such as amino-silanes, epoxy-, aryl- orvinyl silanes are commercially available and, as described above, can beused as additives or can be converted with the reactive constituents ofthe polyol component or of the isocyanate component. In particular,amino-silanes and epoxy-silanes can be easily converted with theisocyanate component.

The method for the production of coated proppants according to thepresent invention can be implemented without the use of solvents.Accordingly, the mixture obtained in step (a) in one embodiment of themethod is solvent-free, or is essentially solvent-free. The mixture isessentially solvent-free, if it contains less than 20 wt %, preferablyless than 10 wt %, more preferably less than 5 wt %, and still morepreferably less than 3 wt %, and most preferably less than 1 wt % ofsolvent, relative to the total mass of components of the mixture.

In step (a) the proppant is preferably heated to an elevated temperatureand then contacted with the coating components. Preferably, the proppantis heated to a temperature within the range of about 50° C. to about150° C. to accelerate crosslinking reactions in the applied coating

The mixer used for the coating process is not particularly restrictedand can be selected from among the mixers known in the specific field.For example, a pug mill mixer or an agitation mixer can be used. Forexample, a drum mixer, a plate-type mixer, a tubular mixer, a troughmixer or a conical mixer can be used. The easiest way is mixing in arotating drum although a continuous mixer or a worm gear can also beused.

Mixing can be carried out on a continuous or discontinuous basis. Insuitable mixers it is possible, for example, to add adhesion agents,isocyanate, amine and optional ingredients continuously to the heatedproppants. For example, isocyanate components, amine reactant andoptional additives can be mixed with the proppant solids in a continuousmixer (such as a worm gear) in one or more steps to make one or morelayers of cured coating.

Preferably, the proppant, isocyanate component, amine reactant and theoptional additives are mixed homogeneously. Thus, the isocyanatecomponent and amine reactant are distributed uniformly on the surface ofthe proppants. The coating ingredients are preferably kept in motionthroughout the entire mixing process. It is also possible to arrangeseveral mixers in series, or to coat the proppants in several runs inone mixer.

The temperature of the coating process is not particularly restrictedoutside of practical concerns for safety and component integrity.Preferably, the coating step is performed at a temperature of betweenabout 10° C. and about 200° C., or more preferably at a temperature ofabout 10° C. to about 150° C.

The coating material may be applied in more than one layer. In thiscase, the coating process is repeated as necessary (e.g. 1-5 times, 2-4times or 2-3 times) to obtain the desired coating thickness and/orsynthetically place the water/hydrocarbon cleaning activity withinlayers on the coated proppant. In this manner, the thickness of thecoating of the proppant can be adjusted and used as either a relativelynarrow range of proppant size or blended with proppants of other sizes,such as those with more or less numbers of coating layers ofpolyurethane according to the present invention, so as to form aproppant blend have more than one range of size distribution. Apreferred range for coated proppant is typically within the range ofabout 20-70 mesh.

The amount of coating resin, that is, of the polyurethane resin appliedto a proppant, is preferably between about 0.5 and about 10 wt %, morepreferably between about 1 and about 5 wt %, resin relative to the massof the proppant as 100 wt %.

The coated proppants can additionally be treated with surface-activeagents or auxiliaries, such as talcum powder or stearate, to improvepourability.

If desired, the coated proppants can be baked or heated for a period oftime sufficient to substantially react at least substantially all of theavailable isocyanate, hydroxyl and reactive amine groups that mightremain in the coated proppant. Such a post-coating cure may occur evenif additional contact time with a catalyst is used after a first coatinglayer or between layers. Typically, the post-coating cure step isperformed like a baking step at a temperature within the range fromabout 100°-200° C. for a time of about 0.5-12 hours, preferably thetemperature is about 125°-175° C. for 0.25-2 hours. Even morepreferably, the coated proppant is cured for a time and under conditionssufficient to produce a coated proppant that exhibits a loss of coatingof less than 25 wt %, preferably less than 15 wt %, and even morepreferably less than 5 wt % when tested according to ISO13503-5:2006(E).

With the method according to the present invention proppants can becoated at temperatures between about 10° C. and about 200° C.,preferably in a solvent-free manner, and combined with a contaminantremoval component such as a NORMS or heavy metal ion exchange orzeolitic material, to effect both stratum fracturing and a measure ofcontaminant removal from the produced water and hydrocarbons while alsoreducing proppant flowback.

Using the Contaminant Removal Proppant Formulation

Furthermore, the invention includes the use of the contaminant removalproppant formulation in conjunction with a fracturing liquid for theproduction of petroleum or natural gas. The fracturing liquid is notparticularly restricted and can be selected from among the frac liquidsknown in the specific field. Suitable fracturing liquids are described,for example, in W C Lyons, G J Plisga, Standard Handbook Of PetroleumAnd Natural Gas Engineering, Gulf Professional Publishing (2005). Thefracturing liquid can be, for example, water gelled with polymers, anoil-in-water emulsion gelled with polymers, a water-in-oil emulsiongelled with polymers or gelled/ungelled hydrocarbon. In one preferredembodiment, the fracturing liquid comprises the following constituentsin the indicated proportions: 1000 1 water, 20 kg potassium chloride,0.120 kg sodium acetate, 3.6 kg guar gum (water-soluble polymer), sodiumhydroxide (as needed) to adjust a pH-value from 9 to 11, 0.120 kg sodiumthiosulfate, and 0.180 kg ammonium persulfate.

In addition, the invention relates to a method for the production ofpetroleum or natural gas which comprises the injection of the coatedproppant into the fractured stratum with the fracturing liquid, i.e.,the injection of a fracturing liquid which contains the coated proppant,into a petroleum- or natural gas-bearing rock layer, and/or itsintroduction into a fracture in the rock layer bearing petroleum ornatural gas. The method is not particularly restricted and can beimplemented in the manner known in the specific field.

When the method of cleaning the water/hydrocarbon makes it mostefficient to use a physical blend of the proppant and one or morecommercial ion exchange resins or zeolites, these blends can be producedat the manufacturing site of the proppant coating process or completedat the wellbore during the fracturing process.

Once those skilled in the art are taught the invention, many variationsand modifications are possible without departing from the inventiveconcepts disclosed herein. The invention, therefore, is not to berestricted except in the spirit of the appended claims.

What is claimed:
 1. A method to remove contaminants from a fracturedwell stratum or well, said method comprising: introducing into saidstratum or said well a solids formulation that comprises first solidparticulates associated with a contaminant removal component in asufficient quantity to remove at least a portion of the contaminants influids in said stratum or well, wherein said contaminant removalcomponent comprises: a. a substantially insoluble coating on said firstsolid particulates that comprises a contaminant removal chemical orbiological agent with a functional affinity for impurities in saidstratum, wherein said chemical comprises at least one sulfonic acid,carboxylic acid, phenolic, amino acid, glycolamine, polyamine,quaternary amine, or polyhydroxylic compound, and/or b. secondparticulates comprising an ion exchange resin, a molecular sieve oractivated carbon that is bound to an outer surface of said proppantparticulate with a substantially insoluble coating.
 2. A methodaccording to claim 1 wherein said second discrete particulate solid is anatural molecular sieve.
 3. A method according to claim 1 wherein saidsecond discrete particulate solid is a synthetic molecular sieve.
 4. Amethod according to claim 1 wherein said second discrete particulatesolid is an ion exchange resin.
 5. A method according to claim 1 whereinsaid removal component is a chemical or biological agent.
 6. A methodaccording to claim 1 wherein said solids are introduced into a gravelpack or a filter sand bed.
 7. A method according to claim 1 wherein saidsubstantially insoluble coating comprises a polyurethane.
 8. A solidsformulation useful for removing contaminants issuing from a fracturedoil and gas production well strata, said solids formulation comprising:a plurality of first particulate solids associated with a contaminantremoval component in sufficient quantity to remove at least a portion ofcontaminants in liquids issuing from a well, wherein said contaminantremoval component comprises (a) a substantially insoluble coating onsaid first particulate solids that comprises a contaminant removalchemical or biological agent with a functional affinity for impuritiesin said stratum, wherein said chemical comprises at least one sulfonicacid, carboxylic acid, phenolic, amino acid, glycolamine, polyamine,quaternary amine, or polyhydroxylic compound, and/or (b) secondparticulate solids comprising an ion exchange resin or a molecular sievethat is bound to an outer surface of said particulate with asubstantially insoluble coating.
 9. A solids formulation according toclaim 8 wherein said contaminant removal component comprises an ionexchange resin.
 10. A solids formulation according to claim 8 whereinsaid contaminant removal component comprises a molecular sieve.
 11. Asolids formulation according to claim 8 wherein said contaminant removalcomponent comprises at least one sulfonic acid.
 12. A solids formulationaccording to claim 8 wherein said contaminant removal componentcomprises at least one carboxylic acid.
 13. A solids formulationaccording to claim 8 wherein said contaminant removal componentcomprises at least one phenolic compound.
 14. A solids formulationaccording to claim 8 wherein said contaminant removal componentcomprises at least one amino acid.
 15. A solids formulation according toclaim 8 wherein said contaminant removal component comprises at leastone glycolamine.
 16. A solids formulation according to claim 8 whereinsaid contaminant removal component comprises at least one polyamine. 17.A solids formulation according to claim 8 wherein said contaminantremoval component comprises at least one quaternary amine.
 18. A solidsformulation according to claim 8 wherein said contaminant removalcomponent comprises at least one polyhydroxylic compound.
 19. A solidsformulation according to claim 8 wherein said contaminant removalcomponent removes contaminants by ionic attraction, ionic exchange,sequestration, amalgamation, chelation, physical entrapment, absorption,adsorption, magnetic attraction, biological degradation, or adhesion.20. A solids formulation according to claim 8 wherein said firstparticulate solids are proppants, gravel pack or filter sand.
 21. Asolids formulation according to claim 8 wherein said substantiallyinsoluble coating comprises a polyurethane.